Photoresist compositions comprising blends of photoacid generators

ABSTRACT

The invention provides new photoresist compositions that contain a resin binder and a blend of photoacid generators. Photoacid generator blends of the invention produce photoacids that differ in acid strength and/or size.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to new photoresist compositions thatcontain a blend of photoacid generator compounds. Compositions of theinvention are highly useful as deep U.V. photoresists.

[0003] 2. Background

[0004] Photoresists are photosensitive films for transfer of images to asubstrate. They form negative or positive images. After coating aphotoresist on a substrate, the coating is exposed through a patternedphotomask to a source of activating energy such as ultraviolet light toform a latent image in the photoresist coating. The photomask has areasopaque and transparent to activating radiation that define an imagedesired to be transferred to the underlying substrate. A relief image isprovided by development of the latent image pattern in the resistcoating. The use of photoresists is generally described, for example, byDeforest, Photoresist Materials and Processes, McGraw Hill Book Company,New York (1975), and by Moreau, Semiconductor Lithography, Principals,Practices and Materials, Plenum Press, New York (1988).

[0005] Known photoresists can provide features having resolution andsize sufficient for many existing commercial applications. However formany other applications, the need exists for new photoresists that canprovide highly resolved images of submicron dimension.

[0006] Various attempts have been made to alter the make-up ofphotoresist compositions to improve performance of functionalproperties. Among other things, a variety of photoactive compounds havebeen reported for use in photoresist compositions. See, e.g., U.S. Pat.No. 4,450,360 and European Application 615163.

[0007] Relatively recently interest has increased in photoresists thatcan be photoimaged with deep U.V. radiation. Such photoresists offer thepotential of forming images of smaller features than may be possible atlonger wavelength exposure. As is recognized by those in the art, “deepU.V. radiation” refers to exposure radiation having a wavelength in therange of about 350 nm or less, more typically in the range of about 300nm or less. While a number of deep U.V. resists have been reported, theneed clearly exists for new deep U.V. resists that can provide highlyresolved fine line images as well as acceptable photospeed and otherlithographic properties. Particular interest exists in resists that canbe imaged with sub-250 nm wavelengths such as KrF radiation (ca. 248 nm)or sub-200 nm wavelengths such as ArF radiation (193 nm).

SUMMARY OF THE INVENTION

[0008] We have now discovered novel blends or mixtures of photoacidgenerators compounds (“PAGs”) that can formulated in photoresistcompositions to provide excellent lithographic properties, particularlychemically-amplified positive-acting resists. Preferred PAG blends canbe photoactivated upon exposure to deep U.V. radiation, particularly 248nm.

[0009] In a first aspect of the invention, PAG blends are provided thatphotogenerate acids of differing strengths. More particularly, preferredPAG blends comprise at least one PAG that generates a strong acid uponphotoactivation, and at least one PAG that generates a comparativelyweak acid upon photoactivation. Typically, the “strong” and “weak”photogenerated acids of the blend differ in pKa values (determined byTaft parameter calculation as discussed in detail below) by at leastabout 1 or 1.5, more typically a pKa difference of at least about 2 ormore. A typical “strong” photogenerated acid of a blend of the inventionhas a pKa (Taft parameter calculation) of about −1 or less, moretypically a pKa of about −2, −3 or lower. A typical “weak”photogenerated acid of a blend of the invention has a pKa (Taftparameter calculation) of about −2, −1, 0 or higher.

[0010] For instance, illustrative preferred “strong” photogeneratedacids include perfluorinated alkylsulfonic acids e.g.perfluorooctanesulfonic acid, perfluorohexanesulfonic acid,perfluorobutanesulfonic acid, perfluoro(4-ethyl)cyclohexanesulfonicacid, trifluoromethanesulfonic acid and the like. Additional suitable“strong” photogenerated acids include aromatic sulfonic acids that aresubstituted with electron withdrawing groups such as fluoro, nitro,cyano and trifluoromethyl. Suitable “strong” photogenerated acids foruse in the blends of the invention may includepentafluorobenzenesulfonic acid, 2-trifluoromethylbenzenesulfonic acid,3-trifluoromethylbenzenesulfonic acid, 4-trifluoromethylbenzenesulfonicacid, and bis(trifluoromethyl)benzenesulfonic acid, particularly3,5-bis(trifluoromethyl) benzenesulfonic acid.

[0011] Preferred “weak” photogenerated acids include e.g. alkylsulfonicacids that are not substituted with electron withdrawing groups such asfluoro, or have minimal electron withdrawing group substitution, e.g.only one or two electron withdrawing substituents. Cycloalkylsulfonicacids are particularly suitable “weak” acids, such ascyclohexanesulfonic acid, adamantanesulfonic acid, camphor sulfonic acidand the like. PAGs that may be employed to provide such acids includee.g. onium salts such as iodonium salts, sulfonium salts and the like;imidosulfonates; sulfonate esters; and non-ionic halogenated compoundsthat generate a halo-acid (e.g. HBr) upon photoactivation.

[0012] In a further aspect, the invention provides PAG blends thatgenerate acids of differing size upon photoactivation. Morespecifically, in this aspect of the invention, preferred PAG blendscomprise at least one PAG that generates a “large” acid uponphotoactivation, and at least one PAG that a comparatively “small” acidupon photoactivation. Typically, the “large” and “small” photogeneratedacids of the blend differ in size by at least about 25 or 30 cubicangstroms (i.e. Å³), more typically by at least about 40 or 50 cubicangstroms (i.e. Å³). A typical “large” photogenerated acid of a blend ofthe invention has a volume of at least about 155 or 160 Å³), morepreferably a volume of at least about 170, 180 or 190 Å³. A typical“small” photogenerated acid of a blend of the invention has a volume ofabout less than 155 or 150 Å³, more preferably a volume of about 130 or140 Å³ or less. Sizes of photogenerated acids may be readily determinedby standard computer-based analyses, as are well-known and furtherdiscussed below.

[0013] PAG blends also are provided that combine both aspects of theinvention, where the blend comprises PAGs that generate acids thatdiffer both in acid strength and size. For example, PAG blends areprovided that comprise at least one PAG that generates uponphotoactivation a strong acid that is large (or small), and at least onePAG that generates upon photoactivation a weak acid that is small (orlarge if the strong acid is small).

[0014] However, in at least some aspects of the invention, it ispreferred that two PAGs of a blend differ only in either size orstrength of the photogenerated acid. Thus, e.g., in this aspect of theinvention, if the blend members generate photoacids that differ in sizeas discussed above, then those photogenerated acid have similar acidstrengths, e.g. a pKa (Taft parmater calculation) difference of 0.5 orless. Similarly, in this aspect of the invention, if the blend membersgenerate photoacids that differ in strength as discussed above, thenthose photogenerated acid have similar size, e.g. less than about 25 or20 Å³ difference in size.

[0015] Without being bound by theory, it is believed that largerphotogenerated acids will diffuse more slowly (relative to a small acid)through a photoresist layer after exposure and prior to development.Such diffusion, particularly into unexposed resist layer areas, canlimit resolution of the developed image. It is also believed that astrong photogenerated acid can provide enhanced photospeed (relative toa weak acid).

[0016] It has been found that selective blending of members of a PAGmixture of the invention can provide the optimal balance of propertiesselected for a particular resist containing the PAG blend.

[0017] Photoresist compositions are also provided that comprise a PAGblend of the invention. PAG blends of the invention can be used in avariety of resist systems. In particular, PAG blends of the inventionare preferably formulated in chemically-amplified positive-actingresists, where the resist contains a polymer with photoacid-labilegroups, particularly pendant acid-labile groups such as can be providedby condensation of alkyl acrylate monomers, e.g. an alkylacrylate-phenol copolymer, or a polymer that contains alkyl acrylaterepeat units and that is essentially or completely free of phenyl orother aromatic units. Unless otherwise indicated, the term acrylate asused herein refers to vinyl esters in general, including substitutedcompounds such as methacrylate and the like.

[0018] It has been that photoresist compositions that contain PAG blendsof the invention can impart significantly improved lithographicproperties to the resist. See, for instance, the comparative results setforth in Examples 2, 3 and 4 which follow. Among other things, it hasbeen found that resists of the invention can provide highly resolvedresist relief images on substrates recognized to compromise resolution,such as boron phosphorus silicate glass. See the results set forth inExample 4 which follows.

[0019] The invention also provide methods for forming relief images ofthe photoresists of the invention, including methods for forming highlyresolved patterned photoresist images (e.g. a patterned line havingessentially vertical sidewalls) of sub-micron and even sub-half microndimensions.

[0020] The present invention further provides articles of manufacturecomprising substrates such as a microelectronic wafer or a flat paneldisplay substrate having coated thereon the photoresists and reliefimages of the invention. Other aspects of the invention are disclosedinfra.

[0021] References herein to pKa values of photoacids designate valuesdetermined by Taft parameter analysis, as such analysis is known in thisfield and described in J. Cameron et al., “Structural Effects ofPhotoacid Generators on Deep UV Resist Performance,” Society of PlasticEngineers, Inc. Proceedings., “Photopolymers, Principles, Processes andMateials, 11^(th) International Conference, pp. 120-139 (1997); and J.P. Gutthrie, Can. J. Chem., 56:2342-2354 (1978). References herein tosizes of photoacids designate volumetric size as determined by standardcomputer modeling, which provides optimized chemical bond lengths andangles. A preferred computer program for determining photoacid size isAlchemy 2000, available from Tripos. For a further discussion ofcomputer-based determination of photoacid size, see T. Omote et al.,Polymers for Advanced Technologies, “Photoreactive Fluorinated PolyimideProtected by a Tetrahydropyranyl Group Based on Photo-inducedAcidolysis”, volume 4, pp. 277-287.

DETAILED DESCRIPTION OF THE INVENTION

[0022] As discussed above, in a first aspect PAG blends are providedthat photogenerate acids of differing strengths e.g. as assessed by pKavalues. In a further aspect, PAG blends are provided that generate uponphotoactivation acids of differing size.

[0023] A variety of PAGs can be employed in the PAG blends andphotoresist compositions of the invention.

[0024] Onium salts are generally preferred PAGs for use in accordancewith the invention. Examples of suitable onium salts include forexample, halonium salts, quaternary ammonium, phosphonium and arsoniumsalts, aromatic sulfonium salts and sulfoxonium salts or selenium salts.Onium salts have been described in the literature such as in U.S. Pat.Nos. 4,442,197; 4,603,101; and 4,624,912.

[0025] Generally preferred onium salts include iodonium salt photoacidgenerators, such as those compounds disclosed in published Europeanapplication 0 708 368 A1. Such salts include those represented by thefollowing formula:

[0026] where Ar¹ and Ar² each independently represents a substituted orunsubstituted aryl group. A preferred example of the aryl group includesa C₆₋₁₄ monocyclic or a condensed ring aryl group. Preferred examples ofthe substituent on the aryl group include an alkyl group, a haloalkylgroup, a cycloalkyl group, an aryl group, an alkoxy group, a nitrogroup, a carboxyl group, an alkoxycarbonyl group, a hydroxyl group,mercapto group, and a halogen atom. Suitable anion substituents Rinclude e.g. R is adamrantane, alkyl (e.g. C₁₋₁₂ alkyl) andperfluoroalkyl such as perfluoro (C₁₋₁₂alkyl), particularly perfluorocounter anions of perfluorooctanesulfonate, perfluorononanesulfonate andthe like.

[0027] Two particularly suitable iodonium PAGs are the following PAGS 1and 2:

[0028] Such compounds can be prepared as disclosed in European PatentApplication 96118111.2 (publication number 0783136), which details thesynthesis of above PAG 1.

[0029] Also suitable are the above two iodonium compounds complexed withanions other than the above-depicted camphor sulfonate groups. Inparticular, preferred anions include those of the formula RSO₃ ⁻ where Ris adamantane, alkyl (e.g. C₁₋₁₂ alkyl) and perfluoroalkyl such asperfluoro (C₁₋₁₂alkyl), particularly perfluoro counter anions ofperfluorooctanesulfonate, perfluorononanesulfonate and the like.

[0030] Sulfonium salts are particularly suitable photoacid generatorsfor PAG blends and resists of the invention, such as compounds of thefollowing formula:

[0031] wherein R³, R⁴ and R⁵ each independently represents a substitutedor unsubstituted alkyl group or aryl group. With regard to each of theabove formulae, preferred examples of the substituted or unsubstitutedalkyl group and aryl group include a C₆₋₁₄ aryl group, a C₁₋₅ alkylgroup, and substituted derivatives thereof. Preferred examples of thesubstituent on the alkyl group include a C₁₋₈ alkoxy group, a C₁₋₈ alkylgroup, nitro group, carboxyl group, hydroxyl group, and a halogen atom.Preferred examples of the substituent on the aryl group include a C₁₋₈alkoxy group, carboxyl group, an alkoxycarbonyl group, a C₁₋₈ haloalkylgroup, a C₅₋₈ cycloalkyl group and a C₁₋₈ alkylthio group. Two of R³, R⁴and R⁵ may be connected to each other via its single bond or asubstituent. R of the above sulfonium formulae may be the same asdefined above for the iodonium PAGs 1 and 2, i.e. adamantane, alkyl(e.g. C₁₋₁₂ alkyl) and perfluoroalkyl such as perfluoro (C₁₋₁₂alkyl),particularly perfluoro counter anions of perfluorooctanesulfonate,perfluorononanesulfonate and the like.

[0032] Additional preferred photoacid generators for use in the blendsand resists of the invention include imidosulfonates such as compoundsof the following formula:

[0033] wherein each R¹ and R^(1′) are each independently hydrogen orC₁₋₁₂ alkyl, more preferably hydrogen or methyl; and R is alkyl (e.g.C₁₋₁₂ alkyl), camphor, adamantane and other cycloalkyl typically havingfrom 5 to about 12 ring members, and perfluoroalkyl such asperfluoro(C₁₋₁₂alkyl), particularly perfluorinated groups such asperfluorooctanesulfonate, perfluorobutanesulfonate and the like. R ofthat formula may be the same as defined above for the iodonium andsulfonium PAGs. A specifically preferred photoacid generator of thisclass is N-[(perfluorooctanesulfonyl)oxy]-5-norbornene-2,3-dicarboximide.

[0034] N-sulfonyloxyimide photoacid generators also are suitable for usein PAG blends and compositions of the invention, including thoseN-sulfonyloxyimides disclosed in International application WO94/10608,such as compounds of the following formula:

[0035] where the carbon atoms form a two carbon structure having asingle, double or aromatic bond, or, alternatively, wherein they form athree carbon structure, that is, where the ring is instead a five memberor six member ring; R is —C_(n)H_(2n+1) where n=1 to 8, —C_(n)F_(2n+1)where n=1 to 8, a camphor substituent, -2(9,10-diethoxyanthracene),—(CH₂)_(n)—Z or —(CF₂)_(n)—Z where n=1 to 4 and where Z is H, Cl, alkyl,a camphor substituent, -2-(9,10-diethoxyanthracene, or aryl such asphenyl; X and Y (1) form a cyclic or polycyclic ring which may containone or more hetero atoms, or (2) form a fused aromatic ring, or (3) maybe independently hydrogen, alkyl or aryl, or (4) may be attached toanother sulfonyloxyimide containing residue, or (5) may be attached to apolymer chain or backbone, or alternatively, form

[0036] where R¹ is selected from the group consisting of H, acetyl,acetamido, alkyl having 1 to 4 carbons where m=1 to 3, NO₂ where m=1 to2, F where m=1 to 5, Cl where m=1 to 2, CF₃ where m=1 to 2, and OCH₃where m=1 to 2, and where m may otherwise be from 1 to 5, andcombinations thereof, and where X and Y (1) form a cyclic or polycyclicring which may contain one or more hetero atoms, (2) form a fusedaromatic ring, (3) may be independently H, alkyl or aryl, (4) may beattached to another sulfonyloxyimide containing residue, or (5) may beattached to a polymeric chain or backbone.

[0037] In certain embodiments of the invention, such N-sulfonyloxyimidesare excluded from PAG blends and resists of the invention, or at leastsuch N-sulfonyloxyimides are excluded from use in combination with asulfonium salt PAG, particularly a triphenyl sulfonium salt, or incombination with an iodonium salt PAG, particularly a diphenyl iodoniumsalt PAG. In certain embodiments, excluded from PAG blends and resistsof the invention will be mixtures of diphenyl-iodonium triflate,di-(t-butylphenyl)iodonium triflate, or phthalimide triflate.

[0038] Another class of photoacid generators suitable for use in theblends and resists of the invention include diazosulfonyl compounds suchas those disclosed in U.S. Pat. No. 5,558,976. Representative examplesof these photoacid generators include:

[0039] where R suitably is phenyl optionally substituted by halogen,C₁₋₈ alkyl, C₁₋₈ alkoxy, or C₁₋₈ haloalkyl; C₁₋₈ alkyl; C₁₋₈ alkoxy; orC₁₋₈ haloalkyl; R⁷ may be the same (e.g. symmetrical compound where Z issulfonyl) or different than R and in addition to the groups specifiedfor R, R⁷ may be a straight-chain, branched or cyclic alkyl group havingfrom 1 to 10 carbon atoms and Z is a sulfonyl group or a carbonyl group:

[0040] where R is as defined above; and

[0041] where R²² is hydrogen, hydroxyl or a group represented by theformula RSO₂O— where R is as defined above, and R²³ is a straight orbranched alkyl group having from 1 to 5 carbon atoms or a grouprepresented by the formula:

[0042] where R²⁴ and R³⁰ are independently a hydrogen atom, a halogenatom, a straight chain or branched alkyl group having 1-5 carbon atoms,a straight chain or branched alkoxy group having 1-5 carbon atoms, or agroup of the formula:

[0043] where each R²⁵ is independently a straight chain or branchedalkyl group having 1-4 carbon atoms, a phenyl group, a substitutedphenyl group or an aralkyl group; and R²⁶ is a hydrogen atom, hydroxy, ahalogen atom or a straight-chain, branched or cyclic alkyl group having1-6 carbon atoms, or alkoxy suitably having 1-6 carbons.

[0044] Nitrobenzyl-based photoacid generators may also be employed as aPAG components of the blends and resists of the invention, includingthose disclosed in EPO published application No. EP 0 717 319 A1.Suitable nitrobenzyl-based compounds include those of the followingformula:

[0045] where each R₁, R₂ and R₃ are individually selected from the groupconsisting of hydrogen and lower alkyl group having from 1-4 carbonatoms; and R₄ and R₅ are individually selected from the group consistingof CF₃ and NO₂ and R is optionally substituted carbocyclic aryl,particularly optionally substituted phenyl such as phenyl where the 2,3, and 4 position substituents are selected from hydrogen and C₁₋₄ alkyland where the 5 and 6 ring positions are selected from CF₃, NO₂ andSO3R′ where R′ of optionally substituted C₁₋₁₂ alkyl or aryl such asphenyl where such optional substituents may be C₁₋₄ alkyl, C₁₋₄ alkoxy,NO₂ or CF₃.

[0046] Disulfone derivatives are also suitable non-ionic photoacidgenerators for use in accordance with the invention. Suitable compoundsare disclosed e.g. in published European application 0 708 368 A1. Suchmaterials may be represented by the following formula:

R—SO₂—SO₂—R′

[0047] wherein R and R′ may each be the same or different and may eachbe the same as defined above for R, or R may be Ar³ where each Arindependently represents a substituted or unsubstituted aryl group. Apreferred example of the aryl group includes a C₆₋₁₄ monocyclic orcondensed-ring aryl group. Preferred examples of the substituent on thearyl group include an alkyl group, a haloalkyl group, a cycloalkylgroup, an aryl group, an alkoxy group, nitro group, carboxyl group, analkoxycarbonyl group, hydroxyl group, mercapto group, and halogen.

[0048] Halogenated non-ionic, photoacid generating compounds are alsosuitable for use in blends and resists of the invention and include, forexample, 1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane (DDT);1,1-bis[p-methoxyphenyl]-2,2,2-trichloroethane;1,2,5,6,9,10-hexabromocyclodecane; 1,10-dibromodecane;1,1-bis[p-chlorophenyl]-2,2-dichloroethane;4,4-dichloro-2-(trichloromethyl) benzhydrol (Kelthane);hexachlorodimethyl sulfone; 2-chloro-6-(trichloromethyl) pyridine;o,o-diethyl-o-(3,5,6-trichloro-2-pyridyl)phosphorothionate;1,2,3,4,5,6-hexachlorocyclohexane;N(1,1-bis[p-chlorophenyl]-2,2,2-trichloroethyl)acetamide;tris[2,3-dibromopropyl]isocyanurate;2,2-bis[p-chlorophenyl]-1,1-dichloroethylene;tris[trichloromethyl]s-triazine; and their isomers, analogs, homologs,and residual compounds. Suitable photoacid generators are also disclosedin European Patent Application Nos. 0164248 and 0232972. Acid generatorsthat are particularly preferred for deep U.V. exposure include1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT);1,1-bis(p-methoxyphenol)-2,2,2-trichloroethane;1,1-bis(chlorophenyl)-2,2,2 trichloroethanol;tris(1,2,3-methanesulfonyl)benzene; and tris(trichloromethyl)triazine.

[0049] PAG blends of the invention may contain more than two differentPAGs, e.g. where multiple PAGs of a single class or type are present ina resist formulation. However, it is often preferred that a PAG blendconsists of no more than two distinct photoacid generators.

[0050] Some specifically preferred photoacids of PAG blends and resistsof the invention are shown immediately with pKa values (Taft parametercalculation) and/or volumetric size values (Å³) listed immediately belowthe acid. CF₃SO₃H CF₃(CF₂)₃SO₃H CF₃(CF₂)₇SO₃H CF₃CF₂SO₃H pK_(a) = −5.21pK_(a) = −5.00 pK_(a) = −4.71 108 A³ 79 A³ 154 A³ 244 A³ CH₃SO₃HCH₃(CH₂)₃SO₃H CH₃(CH₂)₇SO₃H CF₃(CF₂)₅SO₃H pK_(a) = −1.89 pK_(a) = −1.68pK_(a) = −1.41 208 A³ 68 A³

pK_(a) = −1.77 pK_(a) = −1.69 pK_(a) = −1.54 193 A³ 143 A³ 185 A³

pK_(a) = −2.70 pK_(a) = −2.73 pK_(a) = −2.66 140 A³ 137 A³

151 A³ pK_(a) = −3.21 pK_(a) = −3.27

pK_(a) = −2.87 pK_(a) = −2.58 pK_(a) = −3.31

[0051] As discussed above, a PAG blend of the invention is preferablyused in positive-acting chemically amplified resist compositions. Suchcompositions comprise a dissolution inhibitor component, e.g. a resinwith photoacid labile moieties.

[0052] The dissolution inhibitor component may contain any of a varietyof acid labile groups, such as acid sensitive esters, carbonates,acetals, ketals and the like, which suitably may be pendant from apolymer backbone. Acid-labile groups that are integral to the polymerbackbone also may be employed. Preferred deblocking resin binders havealso been disclosed in European Patent Published ApplicationEP0813113A1, European Patent Application 97115532 (corresponding to U.S.Pat. No. 5,861,231), and U.S. Pat. No. 5,258,257 to Sinta et al.Suitable deblocking resins and use of same in chemically amplifiedphotoresists also have been described in U.S. Pat. Nos. 4,968,581;4,883,740; 4,810,613; 4,491,628 and 5,492,793.

[0053] Preferred deblocking resins for use in the resists of theinvention include polymers that contain both phenolic and non-phenolicunits. For example, one preferred group of such polymers has acid labilegroups substantially, essentially or completely only on non-phenolicunits of the polymer. One preferred polymer binder has repeating units xand y of the following formula:

[0054] wherein the hydroxyl group be present at either the ortho, metaor para positions throughout the polymer, and R′ is substituted orunsubstituted alkyl having 1 to about 18 carbon atoms, more typically 1to about 6 to 8 carbon atoms. Tert-butyl is a generally preferred R′group. An R′ group may be optionally substituted by e.g. one or morehalogen (particularly F, Cl or Br), C₁₋₈ alkoxy, C₂₋₈ alkenyl, etc. Thedepicted phenolic units of the polymer also may be optionallysubstituted by such groups. The units x and y may be regularlyalternating in the polymer, or may be randomly interspersed through thepolymer. Such copolymers can be readily formed. For example, for resinsof the above formula, vinyl phenols and a substituted or unsubstitutedalkyl acrylate such as t-butylacrylate and the like may be condensedunder free radical conditions as known in the art. The substituted estermoiety, i.e. R′—O—C(═O)—, of the acrylate units serves as the acidlabile groups of the resin and will undergo photoacid induced cleavageupon exposure of a coating layer of a photoresist containing the resin.Preferably the copolymer will have a Mw of from about 3,000 to about50,000, more preferably about 10,000 to about 30,000 with a molecularweight distribution of about 3 or less, more preferably a molecularweight distribution of about 2 or less. Such copolymers also may beprepared by such free radical polymerization or other known proceduresand suitably will have a Mw of from about 3,000 to about 50,000, and amolecular weight distribution of about 3 or less, more preferably amolecular weight distribution of about 2 or less.

[0055] Additional preferred deblocking resins have acid labile groups onboth phenolic and non-phenolic units of the polymer. One preferredpolymer binder has repeating units a, b and c of the following formula:

[0056] wherein R′ group is a photoacid labile group as defined above forthe other preferred polymer; X is another repeat unit which may or maynot contain a photoacid labile group; and each Y is independentlyhydrogen or C₁₋₆ alkyl, preferably hydrogen or methyl. The values a, band c designate the molar amount of the polymer units. Those polymerunits may be regularly alternating in the polymer, or may be randomlyinterspersed through the polymer. Suitable X groups may be aliphatic oraromatic groups such as phenyl, cyclohexyl, adamantyl, isobomylacrylate,methacrylate, isobornylmethacrylate, and the like. Such polymers may beformed in the same manner as described for the polymer above, andwherein the formed copolymer is reacted to provide the phenolic acidlabile groups.

[0057] Additional preferred deblocking resins include at least threedistinct repeating units of 1) units that contain acid-labile groups; 2)units that are free of reactive groups as well as hydroxy groups; and 3)aromatic or other units that contribute to aqueous developability of aphotoresist containing the polymer as a resin binder. Particularlypreferred deblocking polymers of this type correspond to the followingFormula I:

[0058] wherein R of units 1) is substituted or unsubstituted alkylpreferably having 1 to about 10 carbon atoms, more typically 1 to about6 carbons. Branched alkyl such as tert-butyl are generally preferred Rgroups. Also, the polymer may comprise a mixture of different R groups,e.g., by using a variety of acrylate monomers during the polymersynthesis.

[0059] R¹ groups of units 2) of the above Formula I each independentlymay be e.g. halogen (particularly F, Cl and Br), substituted orunsubstituted alkyl preferably having 1 to about 8 carbons, substitutedor unsubstituted alkoxy preferably having 1 to about 8 carbon atoms,substituted or unsubstituted alkenyl preferably having 2 to about 8carbon atoms, substituted or unsubstituted alkynyl preferably having 2to about 8 carbons, substituted or unsubstituted alkylthio preferablyhaving 1 to about 8 carbons, cyano, nitro, etc.; and m is an integer offrom 0 (where the phenyl ring is fully hydrogen-substituted) to 5, andpreferably is 0, 1 or 2. Also, two R′ groups on adjacent carbons may betaken together to form (with ring carbons to which they are attached)one, two or more fused aromatic or alicyclic rings having from 4 toabout 8 ring members per ring. For example, two RX groups can be takentogether to form (together with the depicted phenyl) a naphthyl oracenaphthyl ring. As with units 1), the polymer may comprise a mixtureof different units 2) with differing R′ groups or no R′ groups (i.e.m=0) by using a variety of substituted or unsubstituted vinylphenylmonomers during the polymer synthesis.

[0060] R² groups of units 3) of the above Formula I each independentlymay be e.g. halogen (particularly F, Cl and Br), substituted orunsubstituted alkyl preferably having 1 to about 8 carbons, substitutedor unsubstituted alkoxy preferably having 1 to about 8 carbon atoms,substituted or unsubstituted alkenyl preferably having 2 to about 8carbon atoms, substituted or unsubstituted sulfonyl preferably having 1to about to about 8 carbon atoms such as mesyl (CH₃SO₂O—), substitutedor unsubstituted alkyl esters such as those represented by RCOO— where Ris preferably an alkyl group preferably having 1 to about 10 carbonatoms, substituted or unsubstituted alkynyl preferably having 2 to about8 carbons, substituted or unsubstituted alkylthio preferably having 1 toabout 8 carbons, cyano, nitro, etc.; and p is an integer of from 0(where the phenyl ring has a single hydroxy substituent) to 4, andpreferably is 0, 1 or 2. Also, two R² groups on adjacent carbons may betaken together to form (with ring carbons to which they are attached)one, two or more fused aromatic or alicyclic rings having from 4 toabout 8 ring members per ring. For example, two R² groups can be takentogether to form (together with the phenol depicted in Formula I) anaphthyl or acenaphthyl ring. As with units 1), the polymer may comprisea mixture of different units 3) with differing R² groups or no R² groups(i.e. p=0) by using a variety of substituted or unsubstitutedvinylphenyl monomers during the polymer synthesis. As shown in Formula Iabove, the hydroxyl group of units 3) may be either at the ortho, metaor para positions throughout the copolymer. Para or meta substitution isgenerally preferred.

[0061] Each R³, R⁴ and R⁵ substituent independently may be hydrogen orsubstituted or unsubstituted alkyl preferably having 1 to about 8 carbonatoms, more typically 1 to about 6 carbons, or more preferably 1 toabout 3 carbons.

[0062] The above-mentioned substituted groups (i.e. substituted groups Rand R₁ through R⁵ of Formula I above) may be substituted at one or moreavailable positions by one or more suitable groups such as halogen(particularly F, Cl or Br); C₁₋₈ alkyl; C₁₋₈ alkoxy; C₂₋₈ alkenyl; C₂₋₈alkynyl; aryl such as phenyl; alkanoyl such as a Cl, alkanoyl of acyland the like; etc. Typically a substituted moiety is substituted at one,two or three available positions.

[0063] In the above Formula I, x, y and z are the mole fractions orpercents of units 3), 2) and 1) respectively in the copolymer. Thesemole fractions may suitably vary over rather wide values, e.g., x may besuitably from about 10 to 90 percent, more preferably about 20 to 90percent; y may be suitably from about 1 to 75 percent, more preferablyabout 2 to 60 percent; and z may be 1 to 75 percent, more preferablyabout 2 to 60 percent.

[0064] Preferred copolymers of the above Formula I include those wherethe only polymer units correspond to the general structures of units 1),2) and 3) above and the sum of the mole percents x, y and z equals onehundred. However, preferred polymers also may comprise additional unitswherein the sum of x, y and z would be less than one hundred, althoughpreferably those units 1), 2) and 3) would still constitute a majorportion of the copolymer, e.g. where the sum of x, y and z would be atleast about 50 percent (i.e. at least 50 molar percent of the polymerconsists of units 1), 2) and 3)), more preferably the sum of x, y and zis at least 70 percent, and still more preferably the sum of x, y and zis at least 80 or 90 percent. See European Published Patent ApplicationEP 0813113A1 for detailed disclosure of free radical synthesis ofcopolymers of the above Formula I.

[0065] Additional resin binders include those that have acetalesterand/or ketalester deblocking groups. Such resins are disclosed in EP0829766A2 of the Shipley Company and U. Kumar. For instance, suitableresins include terpolymers formed from hydroxystryene, styrene and acidlabile components such as 1-propyloxy-1-ethylmethacrylate and the like.

[0066] Additional preferred polymers are disclosed in copending andcommonly assigned U.S. application Ser. No. 09/143,462, filed on Aug.28, 1998.

[0067] Polymers of the invention can be prepared by a variety ofmethods. One suitable method is free radical polymerization, e.g., byreaction of selected monomers to provide the various units as discussedabove in the presence of a radical initiator under an inert atmosphere(e.g., N₂ or argon) and at elevated temperatures such as about 70° C. orgreater, although reaction temperatures may vary depending on thereactivity of the particular reagents employed and the boiling point ofthe reaction solvent (if a solvent is employed). Suitable reactionsolvents include e.g. tetrahydrofuran, dimethylformamide and the like.Suitable reaction temperatures for any particular system can be readilydetermined empirically by those skilled in the art based on the presentdisclosure. Monomers that can be reacted to provide a polymer of theinvention can be readily identified by those skilled in the art based onthe present disclosure. For example, suitable monomers include e.g.acrylate, including methacrylate, t-butylacrylate, acrylonitrile,methacrylonitrile, itaconic anhydride and the like. A variety of freeradical initiators may be employed to prepare the copolymers of theinvention. For example, azo compounds may be employed such asazo-bis-2,4-dimethylpentanenitrile. Peroxides, peresters, peracids andpersulfates also could be employed.

[0068] Unless indicated otherwise above, a polymer used as a resinbinder component of a resist of the invention typically will have aweight average molecular weight (M_(w)) of 1,000 to about 100,000, morepreferably about 2,000 to about 30,000, still more preferably from about2,000 to 15,000 or 20,000, with a molecular weight distribution(M_(w)/M_(n)) of about 3 or less, more preferably a molecular weightdistribution of about 2 or less. Molecular weights (either M_(w) orM_(n)) of the polymers of the invention are suitably determined by gelpermeation chromatography.

[0069] Preferred polymers also will exhibit a sufficiently high T_(g) tofacilitate use of the polymer in a photoresist. Thus, preferably apolymer will have a T_(g) greater than typical softbake (solventremoval) temperatures, e.g. a T_(g) of greater than about 100° C., morepreferably a T_(g) of greater than about 110° C., still more preferablya T_(g) of greater than about 120° C.

[0070] For 193 nm imaging applications, preferably a resist resin bindercomponent will be substantially free of any phenyl or other aromaticgroups. For example, preferred polymers for use in 193 imaging containless than about 1 mole percent aromatic groups, more preferably lessthan about 0.1, 0.02, 0.04 and 0.08 mole percent aromatic groups andstill more preferably less than about 0.01 mole percent aromatic groups.Particularly preferred polymers are completely free of aromatic groups.Aromatic groups can be highly absorbing of sub-200 nm radiation and thusare undesirable for polymers used in photoresists imaged 193 nm.

[0071] Photoresists of the invention also may contain other materials.For example, other optional additives include actinic and contrast dyes,anti-striation agents, plasticizers, speed enhancers, etc. Such optionaladditives typically will be present in minor concentration in aphotoresist composition except for fillers and dyes which may be presentin relatively large concentrations such as, e.g., in amounts of from 5to 30 percent by weight of the total weight of a resist's drycomponents. A preferred additive is a basic compound, such astetrabutylammonium hydroxide (TBAH), tetrabutylammonium lactate, ortetrabutylammonium acetate, which can enhance resolution of a developedimage. For resists imaged at 193 nm, a preferred added base is ahindered amine such as diazabicycloundecene, diazabicyclononene orditerbutylethanolamine. Such an amine may be suitably present in amountof about 0.03 to 5 to 10 weight percent, based on total solids (allcomponents except solvent) of a resist composition.

[0072] The PAG blend component should be present in a photoresistformulation in amount sufficient to enable generation of a latent imagein a coating layer of the resist. More specifically, the PAG blend willsuitably be present in an amount of from about 0.5 to 40 weight percentof total solids of a resist, more typically from about 0.5 to 10 weightpercent of total solids of a resist composition. The distinct PAGs of ablend suitably may be present in about equivalent molar amounts in aresist composition, or each PAG may be present in differing molaramounts. It is typically preferred however that each class or type ofPAG is present in an amount of at least about 20 to 25 mole percent oftotal PAG present in a resist formulation.

[0073] The resin binder component of resists of the invention aretypically used in an amount sufficient to render an exposed coatinglayer of the resist developable such as with an aqueous alkalinesolution. More particularly, a resin binder will suitably comprise 50 toabout 90 weight percent of total solids of the resist.

[0074] The photoresists of the invention are generally preparedfollowing known procedures with the exception that a photoactivecomponent of the invention is substituted for prior photoactivecompounds used in the formulation of such photoresists. For example, aresist of the invention can be prepared as a coating composition bydissolving the components of the photoresist in a suitable solvent suchas, e.g., a glycol ether such as 2-methoxyethyl ether (diglyme),ethylene glycol monomethyl ether, propylene glycol monomethyl ether,propylene glycol monomethyl ether acetate; lactates such as ethyllactate or methyl lactate, with ethyl lactate being preferred;proponiates, particularly methyl propionate, ethyl propionate and ethylethoxy propionate; a Cellosolve ester such as methyl Cellosolve acetate;an aromatic hydrocarbon such toluene or xylene; a ketone such asmethylethyl ketone or cyclohexanone; and the like. Typically the solidscontent of the photoresist varies between 5 and 35 percent by weight ofthe total weight of the photoresist composition.

[0075] The photoresists of the invention can be used in accordance withknown procedures. Though the photoresists of the invention may beapplied as a dry film, they are preferably applied on a substrate as aliquid coating composition, dried by heating to remove solventpreferably until the coating layer is tack free, exposed through aphotomask to activating radiation, optionally post-exposure baked tocreate or enhance solubility differences between exposed and nonexposedregions of the resist coating layer, and then developed preferably withan aqueous alkaline developer to form a relief image.

[0076] The substrate suitably can be any substrate used in processesinvolving photoresists such as a microelectronic wafer. For example, thesubstrate can be a silicon, silicon dioxide or aluminum-aluminum oxidemicroelectronic wafer. Gallium arsenide, ceramic, quartz or coppersubstrates may also be employed. Substrates used for liquid crystaldisplay and other flat panel display applications are also suitablyemployed, e.g. glass substrates, indium tin oxide coated substrates andthe like. As discussed above, it has been found that highly resolvedresist relief images can be formed on substrates that can be difficultto pattern fine images, such as boron phosphorus silicate glass. Aliquid coating resist composition may be applied by any standard meanssuch as spinning, dipping or roller coating.

[0077] Also, rather than applying a resist composition directly onto asubstrate surface, a coating layer of an antireflective coatingcomposition may be first applied onto a substrate surface and thephotoresist coating layer applied over the underlying antireflectivecoating. A number of antireflective coating compositions may be employedincluding the compositions disclosed in European ApplicationsPublication Nos. 0542008A1 and 0813114A2, both of the Shipley Company.For resists to be imaged at 248 nm, an antireflective composition thatcontains a resin binder with anthracene units preferably may beemployed.

[0078] The exposure energy should be sufficient to effectively activatethe photoactive component of the radiation sensitive system to produce apatterned image in the resist coating layer. Suitable exposure energiestypically range from about 10 to 300 mJ/cm². An exposure wavelength inthe deep U.V. range often preferably will be used for the photoresistsof the invention, particularly exposure wavelengths of sub-250 nm orsub-200 nm such as about 248 nm or 193 nm. Preferably, the exposedresist coating layer will be thermally treated after exposure and priorto development, with suitable post-exposure bake temperatures being fromabout e.g. 50° C. or greater, more specifically from about 50 to 160° C.After development, the substrate surface bared by development may thenbe selectively processed, for example chemically etching or platingsubstrate areas bared of photoresist in accordance with procedures knownin the art. Suitable etchants include a hydrofluoric acid etchingsolution and a plasma gas etch such as an oxygen plasma etch.

[0079] All documents mentioned herein are incorporated herein byreference. The following non-limiting examples are illustrative of theinvention.

EXAMPLE 1

[0080] Resist Preparation (Comparative Resists and Resist of theInvention)

[0081] Three photoresist compositions were prepared and are referredherein as Resists 1, 2 and 3 respectively. Each of Resists 1, 2 and 3had the following same components: 1) terpolymer resin havingpolymerized units of hydroxystyrene, styrene and tert-butyl acrylate; 2)additives of tetrabutylammonium hydroxide (0.3 wt. % of terpolymer), acalixresorcinarene (3 wt. % of terpolymer), and surfactant (Silwet L7604at 0.5 wt. % of total solids). Resist 1 (comparative) contained a singlePAG of di-(4-t-butylphenyl)iodonium camphorsulfonate PAG (5 wt. % ofpolymer). Resist 2 contained a PAG blend that consisted of the twocompounds of di-(4-t-butylphenyl)iodonium camphorsulfonate PAG (at 2.5wt. of polymer) and di-(4-t-butylphenyl)iodoniumo-trifluoromethylbenzenesulfonate PAG (at 2.5 wt. % of polymer). Resist3 (comparative) contained a single PAG of di-(4-t-butylphenyl)iodoniumo-trifluoromethylbenzenesulfonate PAG (at 5 wt. % of polymer).

[0082] Each of Resists 1, 2 and 3 were prepared at 16 wt. % solids witha solvent of ethyl lactate, rolled to dissolve, and then filtered to 0.2μm.

EXAMPLE 2

[0083] Lithographic Results

[0084] The lithographic evaluation of these resists was performed andanalyzed as follows.

[0085] Resists 1, 2 and 3 were at room temperature and coated over anorganic antireflective composition coating that had been coated ontounprimed silicon wafers and baked at 225° C. for 60 seconds, yielding a600 angstrom film of the antireflective composition coating layer.Resists 1,2-and 3 were coated to provide approximately 6000 angstromresist coating after a softbake of 130° C. for 60 seconds. Eo photospeedwas determined by exposing a coated wafer of each resist with a 0.1-10.0mJ/cm² dose range using an open-field mask on a GCA XLS7800 Deep UVStepper (248.4 nm krypton fluoride laser, 0.53 numerical aperture, 0.74partial coherence). Each exposed film was post-exposure baked at 130°for 90 seconds and then developed with Ad-10 (2.38% TMA) developer for40 seconds in double puddle mode (20/20 sec. process). The EOphotospeeds of Resists 1, 2 and 3 were 4.3, 3.8, and 3.3 mJ/cm²,respectively. The resists were then tested for imaging performance byproducing dense and isolated contact hole features over an exposurerange beginning at 3×EO, incrementing at 0.1×EO (for 16 steps), andending at approximately 4.6×EO, and over a focus range of 1.8 μm,centered at the machine-determined 0 focus, with 0.15 um increments. Theimaged wafers were analyzed for exposure latitude (EL) for 0.25 μm 1:1contact holes via scanning electron microscopy (SEM). Results are setforth in Table 1 immediately below. TABLE 1 (Energies in mJ/cm²) E0.22Sample Eo E0.22 (Esize) E0.18 EL Es/E0 Resist 1 4.3 15.96 15.03 14.1012.4% 3.50 Resist 2 3.8 14.58 13.60 12.61 14.5% 3.58 Resist 3 3.3 13.0012.49 11.98  8.2% 3.79

[0086] 2. Focus Latitude.

[0087] Focus latitude analysis was performed over the 0.2 μm target CDof the contact holes for each of Resists 1, 2 and 3. Results are setforth in Table 2 immediately below. TABLE 2 Focus Latitude Sample 0.25um Contact Holes Resist 1 0.35 um Resist 2 0.75 um Resist 3  0.5 um

[0088] As can be seen from Tables 1 and 2, Resist 2, which contained aPAG blend of the invention showed the highest exposure latitude andfocus latitude. Hence, that resist of the invention offers an improvedlithographic process window.

EXAMPLE 3

[0089] Additional Lithographic Results

[0090] Two photoresists were prepared and are referred to herein asResists 4 and 5. Each of Resists 4 and 5 had the following samecomponents: 1) terpolymer resin having polymerized units ofhydroxystyrene, styrene and tert-butyl acrylate; 2) additives oftetrabutylammonium hydroxide (0.125 wt. % of terpolymer), and surfactant(Fluorad FC-430 at 0.1 wt. % of total solids). Resist 4 (comparative)contained a single PAG of di-(4-t-butylphenyl)iodoniumo-trifluoromethylbenzenesulfonate PAG (2 wt. % of polymer). Resist 5contained a PAG blend that consisted of the two compounds ofdi-(4-t-butylphenyl)iodonium camphorsulfonate PAG (0.76 wt. % ofpolymer) and di-(4-t-butylphenyl)iodoniumo-trifluoromethylbenzenesulfonate PAG (1.25 wt. % of polymer).

[0091] Each of Resists 4 and 5 were prepared at 16 wt. % solids with asolvent of ethyl lactate, rolled to dissolve, and then filtered to 0.2μm.

[0092] Resist 4 and 5 were each coated, soft-baked, imaged to 248 nmradiation, post-exposure baked and developed as described in Example 2above. The Resists 4 and 5 were exposed to provide for both 0.25 μm and0.20 μm line/space (l/s) pairs and isolated lines (Iso). Exposurelatitude results are set forth in Table 3 below. TABLE 3 1:1 0.25 Iso0.25 1:1 0.20 Iso 0.20 Sample μm l/s μm μm l/s μm Resist 4  7.9% 10.5%2.7% 2.2% Resist 5 14.1% 13.0% 8.3% 8.7   

[0093] As can be seen from the results in Table 3 above, Resist 5(containing a PAG blend of the invention) showed significantly improvedexposure latitude relative to Resist 4, particularly for smallerfeatures where extension of the process window (e.g. exposure latitude)can be critical. In addition, Resist 5 showed significantly higherquality relief image profiles relative to Resist 4.

EXAMPLE 4 Boron Phosphorus Silicate Glass Substrate Application

[0094] Three photoresist compositions were prepared and are referred toherein as Resists 6, 7 and 8. Each of Resists 6, 7, 8 contained acopolymer resin that 65 mole percent hydroxystyrene units and 35 molepercent of tert-butyl acrylate units; tetrabutylammonium hydroxide at0.4 wt. % relative to polymer weight; Silwet L7604 at 0.4 weight %relative to total solids. Resist 6 contained a PAG ofdi-(4-tert-butylphenyl)iodonium camphorsulfonate at 5 weight % relativeto the resin. Resist 7 contained a PAG blend that consisted of 2.5weight % relative to the resin of di-(4-tert-butylphenyl)iodoniumcamphorsulfonate and 2.5 weight % relative to the resin ofdi-(4-tert-butylphenyl)iodonium perfluoroctanesulfonate. Resist 8contained a PAG blend that consisted of 1 weight % relative to the resinof di-(4-tert-butylphenyl)iodonium camphorsulfonate and 4 weight %relative to the resin of di-(4-tert-butylphenyl)iodoniumperfluoroctanesulfonate.

[0095] Each of Resists 6, 7 and 8 were prepared at 16 wt. % solids witha solvent of ethyl lactate, rolled to dissolve, and then filtered to 0.2μm, and then coated onto boron phosphorus silicate glass substrates andbaked at 130° C. for 60 seconds, exposed at 248 nm, 150° C./90 secondpost-exposure bake and 30 second/30 second double puddle alkalineaqueous solution development. Resists 7 and 8 provided fasterphotospeeds (relative to Resist 6), no footing of the developed 0.25 μmcontact hole relief image and greatly reduced standing waves on boronphosphorus silicate glass substrates. The relief image of comparativeResist 6 showed significant footing and severe standing waves.

[0096] The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the spirit or scope of the invention asset forth in the following claims.

What is claimed is:
 1. A photoresist composition comprising: a resinbinder and a mixture of photoacid generator compounds in an amountsufficient to permit development of an exposed coating layer of thecomposition, the photoacid generator compound mixture comprising a firstphotoacid generator and a second photoacid generators, wherein the firstand second photoacid generators generate a first photoacid and a secondphotoacid respectively upon photoactivation that differ in pKa values byat least about 0.5.
 2. The photoresist composition of claim 1 whereinthe first and second photoacid generators generate acids uponphotoactivation that differ in pKa values by at least about
 1. 3. Thephotoresist composition of claim 1 wherein the first and secondphotoacid generators generate acids upon photoactivation that differ inpKa values by at least about 1.5.
 4. The photoresist composition ofclaim 1 wherein the first photoacid has a pKa of about −1 or less. 5.The photoresist composition of claim 1 wherein the first photoacid has apKa of about −2 or less.
 6. The photoresist composition of claim 1wherein the second photoacid has a pKa of about 0 or greater.
 7. Thephotoresist composition of claim 5 wherein the second photoacidgenerator has a pKa of about 0 or greater.
 8. The photoresist of claim 1wherein the first photoacid generator is an onium compound.
 9. Thephotoresist of claim 1 wherein the second ionic photoacid generator isan onium compound.
 10. The photoresist of claim 1 wherein the first orsecond photoacid generator is an imidosulfonate, a diazosulfonylcompound, a sulfonate ester, a nitrobenzyl compound, a disulfonecompound, or a halogenated non-ionic compound.
 11. The photoresist ofclaim 1 wherein the photoacid generated by first or second photoacidgenerator is a perfluoroalkyl sulfonic acid.
 12. The photoresist ofclaim 1 wherein the first and second photoacids differ in size by atleast about 40 Å³.
 13. A photoresist composition comprising: a resinbinder and a mixture of photoacid generator compounds in an amountsufficient to permit development of an exposed coating layer of thecomposition, the photoacid generator compound mixture comprising a firstphotoacid generator and a second photoacid generator, wherein the firstand second photoacid generators generate a first photoacid and a secondphotoacid respectively upon photoactivation that differ in size by atleast about 40 Å³.
 14. The photoresist of claim 13 wherein the first andsecond photoacid generators generate acids upon photoactivation thatdiffer in size by at least about 50 Å³.
 15. The photoresist compositionof claim 13 wherein the first photoacid has a volume of at least about150 Å³.
 16. A method for forming a photoresist relief image on asubstrate comprising: (a) applying a coating layer of a photoresistcomposition of claim 1 on a substrate; and (b) exposing the photoresistcoating layer to patterned activating radiation and developing theexposed photoresist layer to provide a relief image.
 17. A method forforming a photoresist relief image on a substrate comprising: (a)applying a coating layer of a photoresist composition of claim 13 on asubstrate; and (b) exposing the photoresist coating layer to patternedactivating radiation and developing the exposed photoresist layer toprovide a relief image.
 18. An article of manufacture comprising asubstrate having on at least one surface a coating layer of thephotoresist composition of claim 1 .
 19. An article of manufacturecomprising a substrate having on at least one surface a coating layer ofthe photoresist composition of claim 13 .
 20. The article of claim 19wherein the substrate is a microelectronic wafer substrate or a flatpanel display substrate.
 21. A photoacid generator compound mixturecomprising a first photoacid generator and a second photoacidgenerators, wherein the first and second photoacid generators generate afirst photoacid and a second photoacid respectively upon photoactivationthat differ in pKa values by at least about 0.5.
 22. The photoacidgenerator mixture of claim 21 wherein the first and second photoacidsdiffer in size by at least about 40 Å³.
 23. A photoacid generatormixture comprising a first photoacid generator and a second photoacidgenerator, wherein the first and second photoacid generators generate afirst photoacid and a second photoacid respectively upon photoactivationthat differ in size by at least about 40 Å³.